Consumer engagement — Contests like these are perfect for getting people involved with a brand. Not only do they get to do something fun involving McDonald's, but they get to see their ideas showcased on a website and potentially earn a big-time payoff by seeing their sandwich in a McDonald's one day.

Builds hype — It gets the word out for the brand in a social way that can't be replicated by simple print or television ads. The interaction factor inherently makes the contest social — people want to show their friends their awesome ideas.

Product development — McDonald's may get a true winner out of these contests. Its R&D department is constantly churning out more ideas, and they could always use help. The McRibster, for instance, won Austria's "Mein Burger" competition and ended up generating a ton of buzz for McDonald's.

And better yet, some of the key risks involved with crowdsourcing contests are mitigated in McDonald's case. For instance, it doesn't run a risk of angering those that would've gotten the business. Professional designers have grown to hate it when companies try to get work done for free instead of going to them.